Differential sustained attention/vigilance changes over time in schizophrenics and controls during a degraded stimulus Continuous Performance Test

Translational validity of neuropsychological tasks of sustained attention between rodents and humans: A systematic review of three rodent tasks

Atypical sustained attention is a symptom in a number of neurological and psychological conditions. Investigations into its neural underpinnings are required for improved management and treatment. Rodents are useful in investigating the neurobiology underlying atypical sustained attention and several rodent tasks have been developed for use in touchscreen testing platforms that mimic methodology used in human clinical attention assessment. This systematic review was conducted to assess how translatable these rodent tasks are to equivalent clinical human tasks. Studies using the rodent Continuous Performance Task (rCPT), Sustained Attention Task (SAT), and 5-choice CPT (5C-CPT) were sought and screened. Included in the review were 138 studies, using the rCPT (n = 21), SAT (n = 90), and 5C-CPT (n = 27). Translatability between rodent and human studies was assessed based on (1) methodological similarity, (2) performance similarity, and (3) replication of results. The 5C-CPT was found to be the most translatable cross-species paradigm with good utility, while the rCPT and SAT require adaptation and further development to meet these translatability benchmarks. With greater replication and more consistent results, greater confidence in the translation of sustained attention results between species will be engendered.

EEG reveals that dextroamphetamine improves cognitive control through multiple processes in healthy participants

The poor translatability between preclinical and clinical drug trials has limited pro-cognitive therapeutic development. Future pro-cognitive drug trials should use translatable cross-species cognitive tasks with biomarkers (1) relevant to specific cognitive constructs, and (2) sensitive to drug treatment. Here, we used a difficulty-modulated variant of a cross-species cognitive control task with simultaneous electroencephalography (EEG) to identify neurophysiological biomarkers sensitive to the pro-cognitive effects of dextroamphetamine (d-amp) (10 or 20 mg) in healthy adults (n = 23), in a randomized, placebo-controlled, counterbalanced, double blind, within-subject study, conducted across three test days each separated by one week. D-amp boosted d-prime, sped reaction time, and increased frontal P3a amplitude to non-target correct rejections independent of task difficulty. Task difficulty did however, moderate d-amp effects on EEG during target performance. D-amp suppressed frontal theta power during easy target responses which negatively correlated with drug-induced improvement in hit rate while d-amp-induced changes in P3b amplitude during hard target trials strongly correlated with drug-induced improvement in hit rate. In summary, d-amp affected both behavioral and neurophysiological measures of cognitive control elements. Under low-demand, d-amp diminished cognitive control by suppressing theta, yet under high-demand it boosted control in concert with higher P3b amplitudes. These findings thus appear to reflect a gain-sharpening effect of d-amp: during high-demand processes were boosted while during low-demand processes were neglected. Future studies will use these neurophysiological measures of cognitive control as biomarkers to predict d-amp sensitivity in people with cognitive control deficits, including schizophrenia.

Mice lacking melatonin MT2 receptors exhibit attentional deficits, anxiety and enhanced social interaction

BACKGROUND

Aside from regulating circadian rhythms, melatonin also affects cognitive processes, such as alertness, and modulates the brain circuitry underlying psychiatric diseases, such as depression, schizophrenia and bipolar disorder, via mechanisms that are not fully clear. In particular, while melatonin MT1 receptors are thought primarily to mediate the circadian effects of the hormone, the contribution of the MT2 receptor to melatonin actions remains enigmatic.

AIMS

To characterise the contribution of MT2 receptors to melatonin's effects on cognition and anxiety/sociability.

METHODS

Mice with a genetic deletion of the MT2 receptor, encoded by the Mtnr1b gene, were compared with wild-type littermates for performance in a translational touchscreen version of the continuous performance task (CPT) to assess attentional processes and then monitored over 3 days in an ethological home-cage surveillance system.

RESULTS

Mtnr1b knockout (KO) mice were able to perform at relatively normal levels in the CPT. However, they showed consistent evidence of more liberal/risky responding strategies relative to control mice, with increases in hit rates and false alarm rates, which were maintained even when the cognitive demands of the task were increased. Assessment in the home-cage monitoring system revealed that female Mtnr1b KO mice have increased anxiety levels, whereas male Mtnr1b KO mice show increased sociability.

CONCLUSIONS

The results confirm that the MT2 receptor plays a role in cognition and also modulates anxiety and social interactions. These data provide new insights into the functions of endogenous melatonin and will inform future drug development strategies focussed on the MT2 receptor.

Time-on-task effect in trait anhedonia

The capacity to sustain attention was explored in a sample of anhedonic subjects according to the Chapman physical anhedonia scale. Sustained attention was determined by studying task-induced changes over the duration of the Eriksen response competition task [Percept. Psychophys. 16 (1974) 143]. Anhedonic subjects had longer reaction times (RTs), but missed no more targets than control subjects. Anhedonic subject RTs got longer with time-on-task (TOT) and displayed greater intra-subject variability. These results confirm those of a previous study indicating that anhedonic subjects may have developed a more conservative response strategy [Psychophysiology 37 (2000) 711] and suggest that this strategy may result in a more rapid decrease in energetical resources. Moreover, the greater intra-subject variability demonstrates the importance of assessing performance over time and its relationship to the variability of responses in the cognitive performance of anhedonic subjects.

Effects of anterior cingulate cortex lesions on a continuous performance task for mice

Important tools in the study of prefrontal cortical-dependent executive functions are cross-species behavioural tasks with translational validity. A widely used test of executive function and attention in humans is the continuous performance task (CPT). Optimal performance in variations of this task is associated with activity along the medial wall of the prefrontal cortex, including the anterior cingulate cortex (ACC), for its essential components such as response control, target detection and processing of false alarm errors. We assess the validity of a recently developed rodent touchscreen continuous performance task (rCPT) that is analogous to typical human CPT procedures. Here we evaluate the performance of mice with quinolinic acid-induced lesions centred on the ACC in the rCPT following a range of task parameter manipulations designed to challenge attention and impulse control. Lesioned mice showed a disinhibited response profile expressed as a decreased response criterion and increased false alarm rates. ACC lesions also resulted in a milder increase in inter-trial interval responses ('ITI touches') and hit rate. Lesions did not affect discriminative sensitivity d'. The disinhibited behaviour of ACC lesioned animals was stable and not affected by the manipulation of variable task parameter manipulations designed to increase task difficulty. The results are in general agreement with human studies implicating the ACC in the processing of inappropriate responses. We conclude that the rCPT may be useful for studying prefrontal cortex function in mice and has the capability of providing meaningful links between animal and human cognitive tasks.

Sustaining attention to simple visual tasks: a central deficit in schizophrenia? A systematic review

Impairments in sustained attention, that is, the ability to achieve and maintain the focus of cognitive activity on a given stimulation source or task, have been described as central to schizophrenia. Today, sustained attention deficit is still considered as a hallmark of schizophrenia. Nevertheless, current findings on this topic are not consistent. To clarify these findings, we attempt to put these results into perspective according to the type of assessment (i.e., overall and over time assessment), the participants' characteristics (i.e., clinical and demographic characteristics), and the paradigms (i.e., traditionally formatted tasks, go/no-go tasks, and the sustained attention task) and measures used. Two types of assessment lead to opposite findings; they do not evaluate sustained attention the same way. Studies using overall assessments of sustained attention ability tend to reveal a deficit, whereas studies using over time assessments do not. Therefore, further research is needed to investigate the underlying cognitive control mechanisms of changes in sustained attention in schizophrenia.

Mice haploinsufficient for Map2k7, a gene involved in neurodevelopment and risk for schizophrenia, show impaired attention, a vigilance decrement deficit and unstable cognitive processing in an attentional task: impact of minocycline

RATIONALE

Members of the c-Jun N-terminal kinase (JNK) family of mitogen-activated protein (MAP) kinases, and the upstream kinase MKK7, have all been strongly linked with synaptic plasticity and with the development of the neocortex. However, the impact of disruption of this pathway on cognitive function is unclear.

OBJECTIVE

In the current study, we test the hypothesis that reduced MKK7 expression is sufficient to cause cognitive impairment.

METHODS

Attentional function in mice haploinsufficient for Map2k7 (Map2k7 ^+/- mice) was investigated using the five-choice serial reaction time task (5-CSRTT).

RESULTS

Once stable performance had been achieved, Map2k7 ^+/- mice showed a distinctive attentional deficit, in the form of an increased number of missed responses, accompanied by a more pronounced decrement in performance over time and elevated intra-individual reaction time variability. When performance was reassessed after administration of minocycline-a tetracycline antibiotic currently showing promise for the improvement of attentional deficits in patients with schizophrenia-signs of improvement in attentional performance were detected.

CONCLUSIONS

Overall, Map2k7 haploinsufficiency causes a distinctive pattern of cognitive impairment strongly suggestive of an inability to sustain attention, in accordance with those seen in psychiatric patients carrying out similar tasks. This may be important for understanding the mechanisms of cognitive dysfunction in clinical populations and highlights the possibility of treating some of these deficits with minocycline.

Cognitive Translation Using the Rodent Touchscreen Testing Approach

The development of novel therapeutic avenues for the treatment of cognitive deficits in psychiatric and neurodegenerative disease is of high importance, yet progress in this field has been slow. One reason for this lack of success may lie in discrepancies between how cognitive functions are assessed in experimental animals and humans. In an attempt to bridge this translational gap, the rodent touchscreen testing platform is suggested as a translational tool. Specific examples of successful cross-species translation are discussed focusing on paired associate learning (PAL), the 5-choice serial reaction time task (5-CSRTT), the rodent continuous performance task (rCPT) and reversal learning. With ongoing research assessing the neurocognitive validity of tasks, the touchscreen approach is likely to become increasingly prevalent in translational cognitive research.

The continuous performance test (rCPT) for mice: a novel operant touchscreen test of attentional function

RATIONALE

Continuous performance tests (CPTs) are widely used to assess attentional processes in a variety of disorders including Alzheimer's disease and schizophrenia. Common human CPTs require discrimination of sequentially presented, visually patterned 'target' and 'non-target' stimuli at a single location.

OBJECTIVES

The aims of this study were to evaluate the performance of three popular mouse strains on a novel rodent touchscreen test (rCPT) designed to be analogous to common human CPT variants and to investigate the effects of donepezil, a cholinesterase inhibitor and putative cognitive enhancer.

METHODS

C57BL/6J, DBA/2J and CD1 mice (n = 15-16/strain) were trained to baseline performance using four rCPT training stages. Then, probe tests assessed the effects of parameter changes on task performance: stimulus size, duration, contrast, probability, inter-trial interval or inclusion of flanker distractors. rCPT performance was also evaluated following acute administration of donepezil (0-3 mg/kg, i.p.).

RESULTS

C57BL/6J and DBA/2J mice showed similar acquisition rates and final baseline performance following rCPT training. On probe tests, rCPT performance of both strains was sensitive to alteration of visual and/or attentional demands (stimulus size, duration, contrast, rate, flanker distraction). Relative to C57BL/6J, DBA/2J mice exhibited (1) decreasing sensitivity (d') across the 45-min session, (2) reduced performance on probes where the appearance of stimuli or adjacent areas were changed (size, contrast, flanking distractors) and (3) larger dose- and stimulus duration-dependent changes in performance following donepezil administration. In contrast, CD1 mice failed to acquire rCPT (stage 3) and pairwise visual discrimination tasks.

CONCLUSIONS

rCPT is a potentially useful translational tool for assessing attention in mice and for detecting the effects of nootropic drugs.

Paying attention to MMN in schizophrenia

The aim of this review is to explore the phenomenon of reduced mismatch negativity (MMN) in persons with schizophrenia and the possible relationship it has with attention impairments. In doing so we discuss (i) the prediction error account of MMN, (ii) reduced MMN as a faulty predictive processing system in persons with schizophrenia, (iii) the role of these systems in relevance filtering and attentional resource protection, (iv) attentional impairments in persons with schizophrenia, and (v) research that has explored MMN and attention in schizophrenia groups. Our review of the literature suggests that no study has appropriately examined the functional impact of smaller MMN in schizophrenia on the performance of a concurrent attention task. We conclude that future research should explore this notion further in the hope that it might embed MMN findings within outcomes of functional significance to individuals with the illness and those providing treatment. This article is part of a Special Issue entitled SI: Prediction and Attention.

The effect of methylphenidate on sustained attention among adolescents with attention-deficit hyperactivity disorder

Twenty-seven adolescents diagnosed as having attention-deficit hyperactivity disorder (ADHD) were tested twice with a computerized MATH-CPT (mathematics continuous performance test). In one administration, the participants took medication (methylphenidate, MPH) 1.5 hr before being tested. In another administration, the MATH-CPT was administered without the medication. Treatment with MPH improved the "overall attention level" and in measures of "reaction time" and "impulsivity." MPH did not improve the performance in the four measures of sustained attention. Knowing that treatment with MPH does not improve sustained attention can be helpful in reaching a decision of whether or not a child should be treated with MPH.

Impaired limbic cortico-striatal structure and sustained visual attention in a rodent model of schizophrenia

BACKGROUND

N-methyl-d-aspartate receptor (NMDAR) dysfunction is thought to contribute to the pathophysiology of schizophrenia. Accordingly, NMDAR antagonists such as phencyclidine (PCP) are used widely in experimental animals to model cognitive impairment associated with this disorder. However, it is unclear whether PCP disrupts the structural integrity of brain areas relevant to the profile of cognitive impairment in schizophrenia.

METHODS

Here we used high-resolution magnetic resonance imaging and voxel-based morphometry to investigate structural alterations associated with sub-chronic PCP treatment in rats.

RESULTS

Sub-chronic exposure of rats to PCP (5mg/kg twice daily for 7 days) impaired sustained visual attention on a 5-choice serial reaction time task, notably when the attentional load was increased. In contrast, sub-chronic PCP had no significant effect on the attentional filtering of a pre-pulse auditory stimulus in an acoustic startle paradigm. Voxel-based morphometry revealed significantly reduced grey matter density bilaterally in the hippocampus, anterior cingulate cortex, ventral striatum, and amygdala. PCP-treated rats also exhibited reduced cortical thickness in the insular cortex.

CONCLUSIONS

These findings demonstrate that sub-chronic NMDA receptor antagonism is sufficient to produce highly-localized morphological abnormalities in brain areas implicated in the pathogenesis of schizophrenia. Furthermore, PCP exposure resulted in dissociable impairments in attentional function.

Increased distractor vulnerability but preserved vigilance in patients with schizophrenia: evidence from a translational Sustained Attention Task

OBJECTIVE

Attentional deficits represent a core cognitive impairment in schizophrenia. The distractor condition Sustained Attention Task (dSAT) has been identified by the Cognitive Neuroscience Treatment to Improve Cognition in Schizophrenia (CNTRICS) initiative as a promising translational task for assessing schizophrenia-related deficits in attentional selection-control, identifying neuroimaging biomarkers of such deficits, and for preclinical animal research on potential pro-cognitive treatments. Here, we examined whether patients would show specific difficulties in selection-control and in avoiding distraction in the dSAT.

METHOD

Selection-control deficits are measured by comparing attentional performance in the Sustained Attention Task (SAT) without distraction to performance on the task when distraction is present (dSAT). The baseline SAT condition can also be used to assess time-on-task or vigilance effects. Patients with schizophrenia, age- and gender-matched healthy controls and, as an additional control, school-aged children were tested on both the SAT and dSAT.

RESULTS

Compared to healthy controls, patients had reduced performance overall and were differentially vulnerable to distraction. In contrast, patients but not children had preserved vigilance over time.

CONCLUSION

These results demonstrate specific input-selection control impairments in schizophrenia and suggest that patients' distraction-related impairments can be distinguished from general performance impairments and from deficits in other attentional processes (e.g., sustaining attention) evident in other groups.

Sustained attention in intellectually gifted children assessed using a continuous performance test

This study aimed to investigate two aspects of sustained attention in intellectually gifted children: first, the differences to intellectually average children; second, the differences between receiving standard education and enrichment education. Study 1 compared sustained attention between 24 intellectually gifted and 26 intellectually average children. The results showed that intellectually gifted children had better performance than their average peers, not only for the whole task but also on all indices. Study 2 compared sustained attention between 24 intellectually gifted children who received standard education and 24 intellectually gifted children who received enrichment education. The results showed that intellectually gifted children who received enrichment education performed better than those who received standard education. These findings are consistent with previous work and provide support for the implementation of enrichment education for intellectually gifted children.

Kraepelin and Bleuler had it right: people with schizophrenia have deficits sustaining attention over time

An inability to sustain attention was noted in the original clinical descriptions of schizophrenia, but the vast majority of experimental studies have failed to report a performance decrement over time, calling this observation into question. To test for such deficits when task conditions conform to basic science taxonomy for the validity of sustained attention tasks, a dynamic stimulus array was presented in which targets, differing subtly from standard stimuli, were presented infrequently and unpredictably. Both people with schizophrenia (PSZ, n=40) and healthy control subjects (HCS, n=29) displayed a reduction in hit rate and an increase in reaction time (RT) from the first to the second 5-min period. Thereafter, the hit rate of HCS recovered and remained stable, while that of PSZ continued to decline. When performance at task onset was equated between groups, the decrement over time in PSZ remained of the same robust magnitude. Thus, when the nature of the task challenges sustaining attention over time, PSZ display a clear deficit in this ability.

Rats tested after a washout period from sub-chronic PCP administration exhibited impaired performance in the 5-Choice Continuous Performance Test (5C-CPT) when the attentional load was increased

It is well documented that schizophrenia patients exhibit dysfunction in various cognitive domains, including attention/vigilance, as demonstrated by impaired performance in the myriad of Continuous Performance Tests (CPTs). NMDA receptor antagonists provide a pharmacological model in animals of the cognitive disruption presented in the disorder. We therefore examined the effects of a sub-chronic PCP treatment regimen (5.0mg/kg 7-days bi-daily) in the recently developed rodent test of vigilance, the 5-Choice Continuous Performance Test (5C-CPT). We assessed the effects of this regimen after at least a 7-day washout period on both baseline performance and when the attentional load was increased. Sub-chronic PCP treatment impaired 5C-CPT performance in a manner consistent with impaired vigilance in patients with schizophrenia, with reduced hit rate and impaired signal sensitivity. These effects were only evident when performance was challenged following parameter manipulations. These data demonstrate that attention/vigilance is sensitive to disruption following sub-chronic PCP treatment in a pre-clinical task that may demonstrate increased analogy to human vigilance tasks. Although the PCP-induced attentional deficits are not as large as those deficits observed in other domains, these data provide evidence that this pharmacological model can affect multiple cognitive domains and may be useful for assessing putative pro-cognitive therapeutics for schizophrenia.

Interactive effects of background facial emotion stimulus and target salience on sustained attention performance in schizophrenia

Schizophrenia impairs both facial emotion processing and sustained attention. Through separate studies, it is known that the presence of a task-irrelevant facial stimulus disproportionately interferes with performance, whereas increasing the salience of task stimulus improves performance during a sustained attention task in patients with schizophrenia. We wished to investigate a potential interaction effect of background facial emotion expression (black and white happy faces vs. grey oval) and target stimulus salience (bright white vs. grey) using the Continuous Performance Test-Identical Pairs version (CPT-IP) in patients with schizophrenia. Thirty-six patients with schizophrenia and 28 healthy control subjects completed 4 different versions of the CPT-IP. We found that healthy controls exhibited higher signal detection sensitivity (d') when salient target stimuli were presented on the facial background than when the same stimuli were presented on the grey-oval background. By contrast, patients were not affected by background stimuli when target number stimuli were salient. When target number stimuli were not salient, both patients and controls showed higher d' in the grey-oval background condition compared with the facial background condition. This study highlight the significance of stimulus salience during CPT-IP in schizophrenia as background stimuli did not produce a differential effect on performance. Our results suggest that, in the situations where facial emotion stimuli are present, patients' sustained attention can be deteriorated and that the use of salient materials is important in improving performance in schizophrenia.

Sustained attention in the context of emotional processing in patients with schizophrenia

Patients with schizophrenia show dysfunction in sustained attention and facial emotion processing. We investigated the interplay between sustained attention and emotion by presenting emotional faces as background during AX-CPT in patients with schizophrenia. Nineteen schizophrenia patients and 21 healthy control subjects participated. We presented AX-CPT number stimuli superimposed on the nose of background facial expressions (happy, neutral or sad) over three experimental blocks for each emotion. Signal detection sensitivity (A') and reaction time were measured. Patients showed a steeper sensitivity decline when happy faces (compared with sad faces) were presented as background stimuli. By contrast, controls' sensitivity was not affected by the background facial emotion stimuli. Across the emotion conditions, the decline of sensitivity over time was evident in patients, but not in controls. To our knowledge, the present study is the first to explore a change in sustained attention accompanied by simultaneous processing of emotional faces in schizophrenia patients. Our findings suggest that mechanisms underlying continuous performance test (CPT) performance decline over time and facial emotion deficit may interact with each other in patients with schizophrenia.

Dissociation of acute and chronic intermittent phencyclidine-induced performance deficits in the 5-choice serial reaction time task: influence of clozapine

BACKGROUND

Cognitive deficits are a core feature of schizophrenia that respond minimally to existing drugs. PCP is commonly used to model schizophrenia-like deficits preclinically although different dosing protocols may affect different domains. Here we characterise the acute, and chronic intermittent effects of PCP in the 5-choice serial reaction time task (5-CSRTT) in rats, and assess the effects of clozapine. In a novel approach, we also assess the effects of increased inhibitory load and conduct clinically relevant signal detection analysis (SDA).

MATERIALS AND METHODS

The effects of acute and repeated PCP (2.58 mg/kg) treatment on attentional processes and inhibitory control were assessed during and following the chronic treatment regime in the presence or absence of chronic clozapine (20 mg/kg/day).

RESULTS

Thirty minutes post-PCP injection, there was an increase in anticipatory responding which disappeared after 24 h. Although, acute PCP did not change accuracy of responding or processing speed, repeated PCP revealed delayed deficits in cognitive processing speed which were partly ameliorated by clozapine. Extended inter-trial intervals increased premature responding, while SDA revealed that clozapine modified persistent PCP-induced deficits in lnBeta (a composite measure of risk taking versus caution).

CONCLUSION

Acute NMDA receptor antagonism impairs inhibitory control, whereas repeated treatment produces delayed deficits in cognitive processing speed. The ability of clozapine partially to restore persistent PCP-induced deficits in processing speed and in lnBeta is consistent with clinical findings. This suggests that the enduring effects of repeated PCP treatment, combined with SDA, offers a useful, translational, approach to evaluate novel cognitive enhancers in the 5-CSRTT.

Sustained attention as a potential endophenotype for bipolar disorder

OBJECTIVE

Nowadays, it is accepted that to identify the biological basis of psychiatric illnesses it would be useful to deconstruct them into the most basic manifestations, such as cognitive deficits. The aim of this study was to set attention deficit as a stable vulnerability marker of bipolar disorder.

METHOD

Sustained attention was evaluated by the Continuous Performance Test (DS-CPT) in 143 euthymic bipolar patients and 105 controls. To estimate the influence of clinical profile in attention, patients completed a semi-structured interview.

RESULTS

Bipolar patients showed a deficit in attention during euthymic periods. This disturbance correlated with years of evolution, age of onset and age of first hospitalisation; and was not influenced by other clinical data.

CONCLUSION

Sustained attention may be considered as an endophenotype of the illness.

Impaired performance on the Rapid Visual Information Processing task (RVIP) could be an endophenotype of schizophrenia

The aim of the present study was to investigate whether healthy first-degree relatives of schizophrenia patients show reduced sensitivity performance, higher intra-individual variability (IIV) in reaction time (RT), and a steeper decline in sensitivity over time in a sustained attention task. Healthy first-degree relatives of schizophrenia patients (n=23) and healthy control subjects (n=46) without a family history of schizophrenia performed a demanding version of the Rapid Visual Information Processing task (RVIP). RTs, hits, false alarms, and the sensitivity index A' were assessed. The relatives were significantly less sensitive, tended to have higher IIV in RT, but sustained the impaired level of sensitivity over time. Impaired performance on the RVIP is a possible endophenotype for schizophrenia. Higher IIV in RT, apparently caused by impaired context representations, might result in fluctuations in control and lead to more frequent attentional lapses.

Altered brain response without behavioral attention deficits in healthy siblings of schizophrenic patients: an event-related fMRI study

Attention deficits are common in schizophrenics and sometimes reported in their healthy relatives. The aim of this study was to analyse the behavioural performance and the brain activation of healthy siblings of schizophrenic patients during a sustained-attention task. Eleven healthy siblings of schizophrenic patients and eleven matched controls performed a Continuous Performance Test (CPT), during 1.5 T fMRI. The stimuli were presented at three difficulty-levels, using different degrees of degradation (0, 25 and 40%). There were no significant differences in CPT performance (mean reaction time and percentage of errors) between the two groups. Performance worsened with increasing degradation in both groups. Differences were found when comparing the BOLD signal change in the medial frontal gyrus/dorsal anterior cingulate, right precentral gyrus, bilateral posterior cingulate and bilateral insula. The most evident between group differences were observed in the left insula/inferior frontal gyrus: siblings showed a larger activation during wrong responses and a reduced activation during correct responses in the degraded runs. In conclusion, healthy siblings of schizophrenic patients showed differences in brain function in several brain regions previously reported in schizophrenic subjects, in the absence of behavioral attention deficits. The differences were greater in the two more difficult levels of attention demand and might be expressions of altered and/or compensatory mechanisms in subjects at increased risk for schizophrenia.

Baseline [18F]-FDOPA kinetics are predictive of haloperidol-induced changes in dopamine turnover and cognitive performance: A positron emission tomography study in healthy subjects

The telencephalic dopamine innervations contribute to the modulation of cognitive processing. However, the relationship between cognitive effects of D(2/3)-receptor antagonism and dopamine transmission is not described in healthy subjects. We therefore tested effects of acute haloperidol (5 mg/d over 3 days) on continuous performance task (CPT) performance and 6-[(18)F]-fluoro-l-DOPA (FDOPA) PET parameters. Nine physically and mentally healthy male men performed two FDOPA-PET scans including arterial plasma withdrawal. Over 3 days before the second scan, all subjects were treated with 5 mg/d haloperidol orally. Using our novel steady-state analysis, we calculated the intrinsic rate of the cerebral FDOPA utilization (K), the turnover of [(18)F]fluorodopamine formed in brain (k(loss)) and the storage for FDOPA and its brain metabolites (V(d)). Furthermore, a ds-CPT and EPS-screening was performed before every PET scan. We found that FDOPA kinetics in those normal subjects with relatively high baseline K showed a more pronounced sensitivity to haloperidol treatment, manifesting in reduced storage capacity and elevated turnover of [(18)F]fluorodopamine, whereas subjects with lower K showed the opposite pattern of responses. Furthermore, low baseline K predicted improvements in the CPT task after haloperidol, whereas participants with higher baseline K showed a decline in cognitive performance. We conclude that the initial increase of [(18)F]fluorodopamine turnover after acute haloperidol challenge is associated with an over-stimulation in individuals with initially more pharmacologically responsive dopamine systems, but optimizes cognitive performance in those with lower normal FDOPA utilization at baseline. We hypothesize that these effects may be driven by D(1)-receptor mediated transmission during D(2) blockade.

Influence of vigilance and learning on prefrontal activation in schizophrenia

BACKGROUND

Executive functions, which are neuroanatomically associated with the frontal lobe, are known to be impaired in schizophrenia. It is, however, still unclear whether the underlying functional disturbance is due to a hyper- or a hypoactivation of the dorsolateral prefrontal cortex (DLPFC) or neither.

METHODS

To address this question, we examined the brain activation of 21 schizophrenic patients on atypical antipsychotic medication and 21 healthy control subjects during a mental maze task by means of fMRI.

RESULTS

We found no significant overall difference in cerebral activation between the groups, but differences in the change in DLPFC activation from the first to the second half of the experiment. In the maze compared to the control task, there was a decrease in activation in the DLPFC in the patients and an almost significant increase in the controls. The change in activation in the patient group correlated with a change in subjective sleepiness, while the increase in activation in the controls could be attributed to learning processes.

CONCLUSION

We hypothesized that differential temporal influences on brain activation could lead to either hyper- or hypoactivation of the DLPFC in schizophrenia.

Functional dysconnectivity in schizophrenia associated with attentional modulation of motor function

It is not known whether there is a core abnormality that occurs in all cases of schizophrenia. The cognitive dysmetria hypothesis proposes that there is such an abnormality which is characterized cognitively by a disruption in control and coordination processes, and functionally by abnormal inter-regional connectivity within the cortico-cerebellar-thalamo-cortical circuit (CCTCC). In the current study, we used functional MRI (fMRI) to investigate these two key aspects of the hypothesis. Since patients with schizophrenia show deficits in attention which have been characterized extensively using the continuous performance task (CPT) and since functional imaging studies have also demonstrated that this task engages the CCTCC, we used this task to investigate whether two patient groups with distinct symptom profiles would show functional dysconnectivity within this network. Three groups of subjects participated in the study: healthy volunteers (n = 12), schizophrenia patients with both negative and positive symptoms (n = 11) and schizophrenia patients with primarily positive symptoms (n = 11). Patient groups were matched for age of illness onset and medication, and to the control group for age, gender and handedness. Subjects were scanned using fMRI whilst they performed a modified version of the CPT, involving both degraded and non-degraded stimuli. Stimulus degradation has been shown to produce decrements in sensitivity, which is thought to reflect increased demands on the limited capacity of visual attention. Between-group comparisons revealed that patients with schizophrenia, irrespective of symptomatology, showed attenuation of the anterior cingulate and cerebellar response to stimulus degradation in comparison with control subjects. We also observed disruptions of inter-regional brain integration in schizophrenia. A task-specific relationship between the medial superior frontal gyrus and both anterior cingulate and the cerebellum was disrupted in both patient groups in comparison with controls. In addition, patients with negative symptoms showed impaired behavioural performance, and abnormal task-related connectivity between anterior cingulate and supplementary motor area. These findings are consistent with theoretical accounts of schizophrenia as a disorder of functional integration, and with the cognitive dysmetria hypothesis, which posits a disconnection within the CCTCC as a fundamental abnormality in schizophrenia, independent of diagnostic subtype. Furthermore, these data show evidence of additional functional deficits in patients with negative symptoms, deficits which may explain the accompanying attentional impairment.

Effects of lorazepam on the neuromagnetic mismatch negativity (MMNm) and auditory evoked field component N100m

The mismatch negativity (MMN) as an auditory evoked potential is thought to reflect an early, preconscious attention process. While this component has gained great importance in studies on clinical populations and in basic research on auditory information processing, the involvement of different neurotransmitters in the generation of this component is less well understood. We investigated the impact of the benzodiazepine lorazepam as a GABA agonist on the neuromagnetic MMN (MMNm) and auditory evoked field component N100m. A group of 12 healthy subjects was studied in single blind trials under the following three conditions: after the intake of 1.25 mg lorazepam, 100 mg caffeine or placebo. Neuromagnetic recordings were obtained before drug intake and three times after it. Controlled visual attention was tested additionally using a version of the Continuous Performance Test (CPT). The neuromagnetic activity was reconstructed by a single moving dipole, and the dipole moment and its latency were compared between conditions and time points of measurement. Lorazepam diminished the signal detection performance in the CPT 25 min after drug intake. The source of the field component N100m was attenuated, most significantly in the recording 105 min after lorazepam intake. The attenuation of the MMNm under lorazepam became significant at 105 min, but was visually less apparent, because in all conditions a decrease of the MMNm dipole moment within the course of a session was observed. Besides the already known effects of benzodiazepines on controlled attention functions, preconscious attention functions as reflected in the MMN are impaired by acute benzodiazepine intake. MMN studies on clinical populations have to be controlled for the recording time because of the strong habituation of this component.

Attention profile in schizophrenia compared with depression: differential effects of processing speed, selective attention and vigilance

OBJECTIVE

The aim of the study is to investigate whether subjects with schizophrenia and major depression display attention deficits for different reasons.

METHOD

Subjects with schizophrenia (n = 53), recurrent major depression (n = 50) and normal controls (n = 50) were administered with 11 measures of processing speed, selective attention and vigilance. Indices of basal speed, speeded attention, non-speeded attention and vigilance were computed.

RESULTS

Both clinical groups were impaired on all chronometric tests. The schizophrenic subjects were also more impaired on speeded attention compared with basal processing speed. Only the schizophrenics were impaired on the non-speeded measures of selective attention. Compared with the schizophrenics, the depressives showed a decrement in vigilance.

CONCLUSION

Reduced performance on attention tests in major depression is because of a non-specific speed reduction and loss of vigilance consistent with lack of effort. In addition to generally impaired processing speed, the schizophrenic subjects exposed a deficit in selective attention, indicating executive dysfunction.